1. Field of the Invention
The present invention relates to an extrusion molding apparatus for molding a ceramic molded product such as a ceramic honeycomb structure.
2. Description of the Related Art
As shown in FIG. 9 described later, a ceramic honeycomb structure 8 having a plurality of cells 88 with partitioning walls 81 is used, for example, as a catalyst carrier in an exhaust gas purification system of an automotive vehicle. This honeycomb structure 8 is normally fabricated by extrusion molding.
A conventional extrusion molding apparatus 9 for a honeycomb structure, as shown in FIG. 10, for example, comprises a mold 11 for molding the honeycomb structure 8, and screw extruders 92, 93 in two stages, upper and lower, for kneading and extruding a ceramic material 80 continuously.
As shown in FIG. 10, the screw extruders 92, 93 include screws 94, 95 built in housings 929, 939 respectively. By rotating the screws 94, 95, the ceramic material 80 introduced into the housings 929, 939 is extruded by way of an extrusion port at the forward end thereof. The screws 94, 95 include pressure portions 41, 51 formed by spirally winding lead portions 410, 510, and kneading portions 42, 52 having a plurality of disk-shaped flange portions 420, 520, respectively, arranged in spaced relation along the axial direction. Conical forward end portions 945, 955 are arranged on the side of the kneading portions 42, 52 nearer to the forward end extrusion port.
The forward end extrusion ports of screw extruders 92, 93 have filters 62, 63, respectively. A mold 11 is arranged on the forward end port side of the lower screw extruder 93 through a resistance tube 12. The ceramic material 80 is extruded and molded as a honeycomb structure 8 from the mold 11.
The screw extruder may be arranged in a single stage or in three or more stages.
The conventional extrusion molding apparatus 9 described above poses the following problem.
Specifically, the rate at which the ceramic material 80 is extruded from each screw extruder 92, 93 is reflected in the rate at which a ceramic molded product, such as a honeycomb structure 8, is extruded. The higher the extrusion rate of the screw extender, the more efficiently the ceramic molded product can be fabricated.
The extrusion rate of the screw extruders 92, 93 can be increased by increasing the rotational speed of the screws 94, 95. To accomplish this, however, a considerable reconstruction of the equipment drive system is required and cannot be realized readily.
In view of this, development of a technique has been desired for increasing the extrusion rate of the screw extruder efficiently without substantially reconstructing the drive system.
The present invention has been achieved in view of the problem mentioned above, and the object thereof is to provide an extrusion molding apparatus which can increase the rate at which a ceramic material is extruded, without substantial reconstruction of the drive system.